1. Field of the Invention
The invention relates in general to a motherboard of a computer system, and more particularly, the invention relates to a motherboard with reduced power consumption.
2. Description of the Related Art
A normal computer system is basically built with a motherboard, interface cards and peripherals. The motherboard is the base of the computer system, which usually contains a controller chip set, several slots for installing the interface cards, a central processing unit (CPU) and several memory module slots for accommodating the memory modules. A user can install his memory modules offered from different manufacturers with different numbers according to specific requirements, wherein a memory module is typically consisted of several memory devices.
The memory used in a normal computer such as the synchronous dynamic random access memory (SDRAM) operates to control data access in response to the rising edges of the system clock signals. The double data rate (DDR) dynamic random access memory can operate to control the data access on both the rising and falling edges of the system clocks. The DDR DRAM has advantage of performing at the double access rate in comparison with the conventional DRAM due to the upgraded memory access speed.
Modem motherboard systems further comprise a power saving mode. The operation of the DDR DRAM requires a VTT voltage source and several termination resistors to absorb signal reflections from the address, the control and the data signal buses. However, the termination resistors are not isolated from connecting with the voltage source when the conventional computer system enters the power saving mode or before the DDR DRAM module being inserted into the memory module slot. Conventional design for the motherboard system while employing the DDR DRAM obviously consumes powers unnecessarily.
FIG. 1 is a block diagram showing a motherboard of a conventional desktop computer, wherein the motherboard comprises several DDR DRAM memory slots. The address, control and data signal buses of the computer have to connect associated termination resistors to absorb signal reflections for insuring signal transmission qualities on above-mentioned buses when the motherboard of the desktop computer employs DDR DRAM.
Some laptop computer motherboards include DDR SDRAM chips directly soldered onto their motherboards. The soldered memory chips are located near the north bridge chip, so that the signal quality is good even without connecting any termination resistor. However, additional expanded DDR DRAM slots have to connect to termination resistors to prevent signals from poor quality. Although signal transmission quality can be improved after the address, control and data signal buses connect with associated termination resistors, these termination resistors still connect to the voltage source even no DDR DRAM module is inserted in the expanded slot or when a power saving mode is activated. The above two conditions are obviously power-consumptive.